Flow velocimeters (anemometers) are generally known, e.g., laser Doppler velocimeters, which permit a point-for-point measuring of flow fields. These methods are very time-consuming because they are based solely on point-for-point measuring. For that reason, there is a need for whole-field methods in order to simultaneously sense spatial (e.g., three-dimensional) turbulence structures.
Previously, only two-dimensional methods, such as the laser light-sectioning method using real-time vectorization and particle image velocimetry (PIV) were known. However, these methods require a sequential sampling of the flow field, in the sense that three-dimensional structures are examined by arranging a plurality of light sheets side-by-side, which are to be received in time succession.
The disadvantage of these known methods is that they are not applicable to many technically relevant flow problems. This is particularly true when the flow is unsteady and when the velocity components normal to the light sheet (examination plane) are large, and when, due to the lack of optical means, the apparatus configuration does not permit light sheets in the principal flow direction.